Mobile router device, mobile network system, and mobile management method of mobile router device

ABSTRACT

A mobile router device connects a mobile network containing several terminal devices and moving in a backbone network with the backbone network. The mobile router device includes: means for deciding whether to operate as a master router which is a router for actually connecting the mobile network with the backbone network; means for recording a virtual address, a care of address which is an address that the mobile router can use at the moving destination; and means for generating and transmitting a binding update message for correlating the virtual address to the care of address when the mobile router device operates as the master router.

TECHNICAL FIELD

The present invention relates to a mobile router device, to which atleast one terminal device attaches, moving in a backbone network forconnecting the terminal device to the backbone network. It also relatesto a mobile network system containing the mobile router device and theterminal device, and a mobility management method of the mobile routerdevice.

BACKGROUND ART

A communication method of a terminal device moving within the Internetsystem is disclosed as Mobile IPv6 (Mobile Internet Protocol version 6)in a book titled “Detailed Illustration of IPv6 Expert Guide” written byMessrs. Hiroshi Ezaki, Yuji Sekiya, Hideaki Yoshifuji, and TomohiroIshihara, published from Shuwa System Co., Ltd. on May 25, 2002. Therelated article to the present invention appears in this book at page96-99. This protocol allows a terminal device moving between dissimilarnetworks to communicate with others using the same address.

In Mobile IPv6 environment, when a terminal device leaves its home linkto which this device primarily attaches, the device obtains prefixinformation transmitted from an access router of the present link, aboutthe present foreign link, thereby generating a care of address to betemporarily used in the present foreign link from its primary homeaddress and the prefix information.

Then the device transmits a binding update message to its home agent,thereby registering the care of address as a primary care of addresswith the home agent on the home link of the device. The home agentreceives the binding update message from the terminal device, thengenerates or updates a binding cache which associates the home addresswith the care of address.

The home agent refers to the binding cache for receiving, as a proxy forthe terminal device, a packet addressed to the home address on the homelink of the terminal device, then encapsulates the packet for forwardingit to the care of address of the terminal device. The terminal devicedecapsulates the capsule forwarded by the home agent for receiving thepacket originally addressed to its home address.

Mobile IPv6 has been designed with a mobile terminal device in mind;however, not with a mobile network, i.e. it is not assumed that anetwork as a whole moves among different networks. In such a case, aterminal device must carry out the process discussed above for itself.

Japanese patent application non-examined publication No. H09-172451discloses the following communication method of a terminal deviceattached to a mobile network: A virtual IP (VIP) address, i.e. a homeaddress that does not change while the terminal device moves amongvarious networks, is given to the mobile router in addition to anaddress corresponding to a care of address, i.e. an Internet Protocol(IP) address that changes in response to the movement of the device. Thehome agent refers to an address management table (AMT) that associatesthe VIP address with the IP address, then forwards a packet to the IPaddress. This method is hereinafter referred to as a VIP method.

In the VIP method environment, a predetermined mobile router device towhich terminal devices attach, and the home agent that manages the AMTforwards a packet addressed to the terminal device to the IP address ofthe predetermined mobile router, so that the communication is carriedout. The terminal devices within the mobile network need not carry outthe process involved by the movement, so that the movement involves asimpler process in the environment of the VIP method than in theenvironment of Mobile IPv6 method.

However, if the predetermined mobile router device, to which terminaldevices within a mobile network attach, is switched over to anothermobile router, the VIP method requires the respective terminal devicesto carry out the process involved by the movement. To be more specific,plural mobile router devices are prepared on the mobile network as nodesbetween an access router on the Internet and the mobile network. If adefective is found in a present mobile router device or if a connectionis lost between the Internet and the present mobile router device, thepresent mobile router device is switched to another mobile routerdevice, so that the another one takes over the function of the presentone. At this time, the predetermined mobile router loses the connectionto the terminal devices, and the terminal devices move to this anothermobile router device. Therefore, the respective terminal devices mustcarry out the process for associating their home addresses with care ofaddresses to their home agent. This process increases the load to thenetwork, and it is impossible for all the terminal devices to registerphysical addresses, so that it takes a considerably long time for someterminal devices to register the physical address with the home agent.

DISCLOSURE OF INVENTION

In a mobile network that moves among plural access networks forconnecting its terminal devices to a backbone network, and under theenvironment where plural mobile router devices are prepared in themobile network for connecting the mobile network to the access networks,the present invention aims to provide a mobile network system, a mobilerouter device, and a mobility management method of the mobile routerdevice, which can switch over the mobile router device withoutincreasing a load to the network.

In order to achieve the foregoing objective, the mobile router device ofthe present invention connects a backbone network to a mobile network towhich at least one terminal device attaches and moves within thebackbone network. The mobile router device of the present inventioncomprises the following elements:

-   -   a means for determining whether or not the router device        actually works as a master router that can connects the mobile        network to the backbone network;    -   a means for recording a virtual address common to all the mobile        router devices attaching to the mobile network, and originating        a care of address, usable at a location to where the mobile        router is connected, corresponding to the virtual address; and    -   a means for originating and transmitting a binding update        message that associates the virtual address with the care of        address in the case of working the mobile router device as the        master router device.

The structure discussed above allows eliminating the transmission of thebinding update message for erasing obsolete information in the bindingcache to be used for the mobile router device switched over to anotherone to manage the location information of the mobile router devices atthe home agent, even if the mobile router device is switched over toanother one in the mobile network. Actually a mobile router device,which carries out the connection to the Internet, simply updates thebinding to the home network by using the same virtual address, therebymaintaining the communication between a terminal device in the mobilenetwork and a correspondent node device.

At the home agent in the home network, the home address corresponding tothe care of address, which indicates a location to where the mobilerouter device is connected, stays uniquely regardless of a switch overto another mobile router device, so that a distribution route needs nochanges.

In the mobile router device of the present invention, a real addressassigned to any one of respective mobile router devices attaching to themobile network is used as a virtual address. This structure eliminatesthe need of providing a new common address, thereby taking less space inan address space. A non-functional mobile router device having noaddress pre-assigned can work as a functional mobile router device byusing the virtual address.

A mobile router device of the present invention comprises the followingelements:

-   -   a means for monitoring the quality of a link connecting to a        backbone network;    -   a means for changing a priority of determining a master router        and a backup router in response to the quality of the link; and    -   a means for determining whether or not the router works as a        master router in response to the priority.        The structure discussed above allows the mobile router device        having the best connection quality to the backbone network to        work as a master router, so that a high quality communication        can be expected while the router moves.

A mobile router device of the present invention includes a means fortransmitting master router advertisement packet which stores a sequencenumber of a binding update message in case of the mobile router deviceis working as a master router. This structure allows inheriting anupdated sequence number for processing the binding update, even when themobile router device, which updates the binding to the home agent, isswitched over to another one among plural mobile router devices providedin a mobile network. As a result, it can be guaranteed that the messagecontains updated information, and the home agent can be prevented fromdisposing of the information as obsolete one.

A mobile router device of the present invention comprises the followingelements while it works as a backup router:

-   -   a means for receiving a master router advertisement packet        transmitted by another mobile router device to notify that the        router device is working as a master router; and    -   a means for recording a sequence number of a binding update        message contained in the master router advertisement packet        received in order to use the number when it works as the master        router.        This structure allows inheriting an updated sequence number for        processing the binding update, even when the mobile router        device, which updates the binding to the home agent, is replaced        with another one among plural mobile router devices provided in        a mobile network. As a result, it can be guaranteed that the        message contains updated information, and the home agent can be        prevented from disposing of the information as obsolete one.

A mobile router device of the present invention allows a master routeradvertisement packet to use a virtual advertisement specified by avirtual router redundancy protocol. This structure prevents the mobilerouter device using a virtual router redundancy protocol fromtransmitting a new message in order to notify other mobile routerdevices of an updated sequence number. As a result, it can be avoidedthat the number of messages to be transmitted in the mobile networkincreases.

A mobile router device of the present invention allows a master routeradvertisement packet to use an Ipv6 router advertisement message. Thisstructure allows preventing the mobile router device working as a routerdevice from transmitting a new message in order to notify other mobilerouter devices of an, updated sequence number. As a result, it can beavoided that the number of messages to be transmitted in the mobilenetwork increases.

A mobile network system of the present invention comprises the followingelements:

-   -   plural mobile router devices;    -   at least one terminal device attached to the mobile router        devices; and

a home agent device for managing a movement of the mobile routerdevices.

When a mobile router device cannot be connected to a backbone networkbut another one can be connected thereto, this structure allowsswitching the mobile router device to another one for maintaining thecommunication without adding a new process or a function to the terminaldevices or the home agent.

A mobile network system of the present invention includes mobile routerdevices, and at least one of the devices has a different type ofphysical interface to the backbone network from those of the othermobile router devices. This structure allows maintaining thecommunication while the mobile network moves among various types ofaccess networks.

A mobile network system of the present invention allows respectivemobile router devices to use a common virtual address at the interfaceto the backbone network, and implement a virtual router redundancyprotocol for the mobile network. The structure also allows a mobilerouter device working as a master router to use the common virtualaddress. This structure allows a home address, corresponding to a careof address indicating a location where a mobile router device has moved,to become unique regardless of switch over to another mobile routerdevice. As a result, a change in a setting of a distribution route isnot needed, and the switch over of the mobile router device does notinvolve any change in the terminal devices within the mobile network.

A mobile network system of the present invention allows that the mobilerouter which works as a master router transmits a binding update messageto the home agent device. This binding update message includes a commonvirtual address and care of address generated corresponding to thecommon virtual address, and is to be used by a home agent for managingthe movements of the mobile network. When a mobile router device isswitched over to another one, this structure allows eliminating thenecessity of transmitting a binding update message for erasing obsoleteinformation in a biding cache used by the mobile router device switchedover to another one for managing the location information of the mobilerouter devices at the home agent. This structure allows thatcorrespondent terminal device can maintain communication with a terminaldevice in the mobile network by only the mobile router device whichactually connected to the Internet carrying out the binding updateprocessing to the home network using the common virtual address. At thehome agent in the home network, a home address corresponding to a careof address indicating where the mobile router device has moved becomesunique regardless of a switch over to a mobile router device, so that nochange is required in a setting of the distribution route.

A mobility management method of mobile router device of the presentinvention manages movements of a mobile router device in a mobilenetwork system, which system comprises the following elements:

-   -   a mobile network including at least one terminal device and        plural mobile router devices, to which the terminal device        attaches, for connecting the terminal devices to a backbone        network; and    -   a home agent device that manages a home address and a care of        address by associating those addresses with each other.

When a mobile network is coupled to its home network, a virtual addressto be used in a physical interface of the mobile network connected tothe backbone network and to be generated after the movement of a mobilerouter device working as a master router and a care of addresscorresponding to the virtual address are registered with the home agentdevice by associating those addresses with each other. When a mobilerouter having worked as a backup router is switched over to working as amaster router, a care of address corresponding to a virtual address andbeing generated after the change is associated with the virtual addressand registered with the home agent device.

When the mobile network moves and the mobile router device that actuallyconnects other mobile router devices to the backbone network is switchedover to another one, the method discussed above allows the home agent tomanage a plurality of mobile router devices as one mobile router device,i.e. equivalent to the case where the present mobile router devicemoves. As a result, a change in a setting of the distribution route isnot needed.

In the case of switching over a mobile router device used in a mobilenetwork to another one, this method allows eliminating the necessity oftransmitting a binding update message for erasing obsolete informationin a biding cache used by the mobile router device switched over toanother one for managing the location information of the mobile routerdevices at the home agent. This structure allows that correspondentterminal device can maintain communication with a terminal device in themobile network by only the mobile router device which actually connectedto the Internet carrying out the binding update processing to the homenetwork using a common virtual address.

A mobility management method of mobile router device of the presentinvention allows a virtual address to be any one of physical addressesto be used in respective mobile router devices attaching to a mobilenetwork at their physical interfaces on their sides to the backbonenetwork when they are to be coupled to their home network. Thisstructure eliminates the need of providing a new common address, therebytaking less space in an address space. A non-functional mobile routerdevice having no address assigned can work as a functional mobile routerdevice using the virtual address.

A mobility management method of mobile router device of the presentinvention allows a master router advertisement packet, which istransmitted to the mobile network in order to notify the mobile routerdevice works as a master router, to include the virtual address and asequence number of a binding update message to be transmitted to thehome agent device. This method allows inheriting an updated sequencenumber for processing the binding update, even when the mobile routerdevice, which updates the binding to the home agent, is switched over toanother one. As a result, it can be guaranteed that the message containsupdated information, and the home agent can be prevented from disposingof the information as obsolete one.

A mobility management method of mobile router device of the presentinvention allows a master router advertisement packet to be a virtualadvertisement packet to be used by a virtual router redundancy protocolcarried out in the mobile router device at the mobile network side. Thisstructure prevents respective mobile router devices using a virtualrouter redundancy protocol from transmitting a new message in order tonotify other mobile router devices of an updated sequence number. As aresult, it can be avoided that the number of messages to be transmittedin the mobile network increases.

A mobility management method of mobile router device of the presentinvention allows a master router advertisement packet to be an IPv6router advertisement message which is transmitted by the mobile routerdevice, working as a master router, to its mobile network side. Thismethod allows preventing the mobile router device working as a masterrouter device from transmitting a new message in order to notify othermobile router devices of an updated sequence number. As a result, it canbe avoided that the number of messages to be transmitted in the mobilenetwork increases.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a diagram illustrating a network system in accordance witha first exemplary embodiment of the present invention.

FIG. 2 shows a diagram illustrating a case where a mobile network leavesits home network in the network system in accordance with the firstexemplary embodiment of the present invention.

FIG. 3 shows a diagram illustrating a case where a mobile router device,which connects the mobile network to the Internet, is switched over toanother one in the network system in accordance with the first exemplaryembodiment of the present invention.

FIG. 4 shows a block diagram illustrating a structure of a mobile routerdevice in accordance with the first exemplary embodiment of the presentinvention.

FIG. 5 shows a flowchart illustrating a process flow of updating abinding in accordance with the first exemplary embodiment of the presentinvention.

FIG. 6 shows a structure of a binding update message in accordance withthe first exemplary embodiment of the present invention.

FIG. 7A shows a format of a home address option in the binding updatemessage in accordance with the first exemplary embodiment of the presentinvention.

FIG. 7B shows a format of a mobility header in the binding updatemessage in accordance with the first exemplary embodiment of the presentinvention.

FIG. 7C shows a format of a binding update in the binding update messagein accordance with the first exemplary embodiment of the presentinvention.

FIG. 7D shows a format of an alternate care of address mobility optionin the binding update message in accordance with the first exemplaryembodiment of the present invention.

FIG. 8 shows a structure of a binding update message in accordance withthe first exemplary embodiment of the present invention.

FIG. 9A shows a format of a home address option in the binding updatemessage in accordance with the first exemplary embodiment of the presentinvention.

FIG. 9B shows a format of a mobility header in the binding updatemessage in accordance with the first exemplary embodiment of the presentinvention.

FIG. 9C shows a format of a binding update in the binding update messagein accordance with the first exemplary embodiment of the presentinvention.

FIG. 9D shows a format of an alternate care of address mobility optionin the binding update message in accordance with the first exemplaryembodiment of the present invention.

FIG. 10 shows a block diagram illustrating a structure of a mobilerouter device in accordance with the first exemplary embodiment of thepresent invention.

FIG. 11 shows a sequence diagram illustrating a mobility managementmethod in accordance with the first exemplary embodiment of the presentinvention.

FIG. 12 shows a structure of a router advertisement message inaccordance with the first and the second exemplary embodiments of thepresent invention.

FIG. 13A shows a format of the router advertisement message inaccordance with the first and the second exemplary embodiments of thepresent invention.

FIG. 13B shows a format of a prefix information option in the routeradvertisement message in accordance with the first and the secondexemplary embodiments of the present invention.

FIG. 13C shows a format of an advertisement interval option in therouter advertisement message in accordance with the first and the secondexemplary embodiments of the present invention.

FIG. 13D shows a format of a sequence number of a binding message in therouter advertisement message in accordance with the first and the secondexemplary embodiments of the present invention.

FIG. 14 shows a structure of a binding cache in accordance with thefirst exemplary embodiment of the present invention.

FIG. 15 shows a sequence diagram illustrating a mobility managementmethod in accordance with the first exemplary embodiment of the presentinvention.

FIG. 16 shows a structure of a binding cache in accordance with thefirst exemplary embodiment of the present invention.

FIG. 17 shows a diagram illustrating a network system in accordance withthe first exemplary embodiment of the present invention.

FIG. 18 shows a diagram illustrating a case where a mobile networkleaves its home network in the network system in accordance with thesecond exemplary embodiment of the present invention.

FIG. 19 shows a diagram illustrating a case where a mobile routerdevice, which connects the mobile network to the Internet, is switchedover to another one in the network system in accordance with the secondexemplary embodiment of the present invention.

FIG. 20 shows a block diagram illustrating a structure of a mobilerouter device in accordance with the second exemplary embodiment of thepresent invention.

FIG. 21 shows a flowchart illustrating a process flow of updating abinding in accordance with the second exemplary embodiment of thepresent invention.

FIG. 22 shows a structure of a binding update message in accordance withthe second exemplary embodiment of the present invention.

FIG. 23A shows a format of a home address option in the binding updatemessage in accordance with the second exemplary embodiment of thepresent invention.

FIG. 23B shows a format of a mobility header in the binding updatemessage in accordance with the second exemplary embodiment of thepresent invention.

FIG. 23C shows a format of a binding update in the binding updatemessage in accordance with the second exemplary embodiment of thepresent invention.

FIG. 23D shows a format of an alternate care of address mobility optionin the binding update message in accordance with the second exemplaryembodiment of the present invention.

FIG. 24 shows a block diagram illustrating a structure of a mobilerouter device in accordance with the second exemplary embodiment of thepresent invention.

FIG. 25 shows a sequence diagram illustrating a mobility managementmethod in accordance with the second exemplary embodiment of the presentinvention.

FIG. 26 shows a structure of a binding cache in accordance with thesecond exemplary embodiment of the present invention.

FIG. 27 shows a sequence diagram illustrating a mobility managementmethod in accordance with the second exemplary embodiment of the presentinvention.

FIG. 28 shows a structure of a binding cache in accordance with thesecond exemplary embodiment of the present invention.

FIG. 29 shows a sequence diagram of a virtual router redundancy protocolin accordance with the second exemplary embodiment of the presentinvention.

FIG. 30 shows a format of a VRRP field in accordance with the secondexemplary embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Exemplary embodiments of the present invention are demonstratedhereinafter with reference to the accompanying drawings.

Exemplary Embodiment 1

FIG. 1 shows a diagram illustrating a mobile network system inaccordance with the first exemplary embodiment of the present invention.In FIG. 1, mobile network 1 connected to home network 20 is connected tothe Internet 8 (backbone network) via home gateway 7. Mobile network 1includes mobile router devices MR2, MR3 (sometimes referred to as mobilerouters 2, 3), and terminal device LFN5. Mobile router devices MR2 andMR3 have the same physical interfaces with each other or differentphysical interfaces from each other at their sides to backbone network8.

Those interfaces can adopt Ethernet method, IEEE802.11 (a, b, e, g,etc.) method, HIPERLAN method, IMT-2000 method, PDC method, GPRS method,or PHS method. Interfaces at their sides to the mobile network can adoptEthernet method, Bluetooth method, Ultra Wide Band (UWB) method, orIEEE802.11 (a, b, e, g, etc.).

In the case of an instance shown in FIG. 1, mobile network 1 isconnected to home network 20 via mobile router device MR2, and mobilerouter device MR3 is connected to mobile network 1 with the physicalinterface to the mobile network but the physical interface to thebackbone network is left open. The physical interface to the backbonenetwork 8 of mobile router device MR2 has an address of MR2_HoA, and thephysical interface to mobile network 1 has an address of MR2_In whilethe physical interface to mobile network 1 of MR3 has an address ofMR3_In.

Mobile router device MR2, which connecting home network 20 to mobilenetwork 1, transmits router advertisement message 1010 shown in FIG. 13Ato mobile network 1. Meanwhile, option field 1020 of this routeradvertisement message 1010 includes, as shown in FIG. 12, prefixinformation option 1030 shown in FIG. 13B. Thus the default routeraddress of terminal device LFN5 is MR2_In corresponding to router MR2,and home gateway HGW7 transmits the packet to MR2_HoA before the packetreaches to mobile network 1.

When a correspondent node device CN11 with which a terminal device ormobile router device is communicating transmits a packet addressed toterminal device LFN5, the packet transmitted arrives at home gatewayHGW7 based on the route information in the Internet 8. Home gateway HGW7transmits the packet addressed to mobile network 1 to address MR2_HoA.Mobile router device MR2 then forwards the packet addressed to terminaldevice LFN5 to network 1, then the packet arrives at terminal deviceLFN5.

On the other hand, terminal device LFN5 transmits a packet tocorrespondent node device CN11 this way: Terminal device LFN5 transmitsa packet addressed to correspondent node device CN11 to address MR2_Inof a default router, namely, mobile router device MR2. Device MR2receives the packet and determines whether or not the destination of thepacket belongs to home network 20. Since correspondent node device CN11does not attach to home network 20, MR2 then forwards the packet to homegateway HGW7, which then forwards the packet to the Internet 8 becausethe destination of the packet does not belong to its own home network20. The packet then transmitted to correspondent node device CN11 viathe Internet 8.

A connecting point to the Internet 8 is changed because mobile network 1moves. A mobility management method in this case is demonstrated withreference to FIG. 2 and FIG. 11. As shown in FIG. 2, mobile network 1leaves home network 20 and attaches to access router AR9 of whichphysical link is common to mobile router device MR2 as the physicalinterface to the backbone network (S901). At this time, MR2 receives arouter advertisement message transmitted from access router AR9 (S902).Router MR2 generates care of address MR2_CoA to be temporarily usedunder router AR9 by using the prefix information contained in the routeradvertisement message (S903).

FIG. 13A-FIG. 13D show a format of router advertisement message 1010.Option field 1020 of router advertisement message 1010 shown in FIG. 13Aincludes prefix information option 1030 shown in FIG. 13B andadvertisement interval option 1050 shown in FIG. 13C.

Next, mobile router device MR2 generates binding update message 600 thatstores home address MR2_HoA 603 and care of address MR2_CoA 634 shown inFIG. 6 and FIGS. 7A-7D (S904), then transmits message 600 to home agentHA6 (S905). After this, device MR2 registers its care of address MR2_CoAas a primary care of address with home agent HA6 on home network 20 ofmobile network 1.

Home agent HA6 receives binding update message 600, then generatesbinding cache 1100 which associates home address MR2_HoA with care ofaddress MR2_CoA (S906). This completes the preparation for forwarding orredirecting a packet to mobile network 1 after the movement of mobilenetwork 1 from home network 20 (S907). FIG. 14 shows an instance ofbinding cache 1100 with which home address 1101, care of address 1102,lifetime 1103, flag 1104, sequence number 1105, and usage information1106 are associated with each other and registered.

Mobile router device MR2 further generates a router advertisementmessage including binding message sequence number option 1070 in optionfield 1020 of router advertisement message 1010 in addition to prefixinformation option 1030, then transmits the message to mobile network 1.A mobile router device attaching to mobile network 1 receives routeradvertisement message 1010 including binding massage sequence numberoption 1070, then records the sequence number.

The packet addressed to terminal device LFN5 and transmitted fromcorrspondent node device CN11 arrives at home gateway HGW7 based on theroute information in the Internet 8. Home gateway HGW7 transfers thepacket addressed to mobile network 1 to address MR2_HoA.

However, since home agent HA6 includes binding cache 1100 of MR2_HoA andcare of address MR2_CoA, home agent HA6 intercepts the packet, andencapsulates the packet addressed to terminal device LFN5, then forwardsthe capsule to care of address MR2_CoA of mobile router device MR2. Thepacket encapsulated is delivered to mobile router MR2 via access routerAR9, and decapsulated by MR2 before the packet is forwarded to terminaldevice LFN5.

On the other hand, terminal device LFN5 transmits a packet tocorrespondent node device CN11 this way: Terminal device LFN5 transmitsa packet addressed to correspondent node device CN11 to address MR2_Inof a default router, namely, mobile router device MR2. Device MR2receives the packet addressed to CN11, then encapsulates the packet andforwards the capsule to home agent HA6.

The packet encapsulated is delivered to home agent HA6 via access routerAR9, then decapsulated by home agent HA6. An examination of the packetaddress finds that the address does not belong to home network 20, sothat the packet is forwarded to correspondent node device CN11 via theInternet 8.

Next, when mobile router device MR2 cannot find a usable access link butmobile router device MR3 finds the usable access link, what kind ofmobility management method is taken is demonstrated hereinafter withreference to FIG. 3 and FIG. 15. As shown in FIG. 3, it is assumed thatmobile network 1 leaves home network 20 or access network 21, and entersunder access router AR 10 having a physical link as same as the physicalinterface to the backbone network interface of mobile router device MR3(S1201).

At this time, after mobile router device MR2 has received routeradvertisement message 1010 transmitted from access router AR9, if routerMR2 cannot receive the next router advertisement message 1010 in a timesubstantially longer than router advertisement interval 1054 (e.g.advertisement interval×3) included in router advertisement message 1010,router MR2 determines that the connection to access router AR9 is lost.

Mobile router device MR3 receives router advertisement message 1010transmitted from access router AR10 (S1202). Router MR3 obtains prefixinformation 1043 from router advertisement message 1010, and generatescare of address MR3_CoA to be temporarily used under access router AR10(S1203).

Next, mobile router device MR3 detects the halt of periodicaltransmission of router advertisement message 1010 from router MR2. Aftermobile router MR3 has received the updated router advertisement message1010 transmitted from router MR2, if router MR3 cannot receive the nextrouter advertisement message 1010 in a time substantially longer thanrouter advertisement interval 1054 (e.g. advertisement interval×3)included in router advertisement message 1010, router MR3 determinesthat the periodical transmission of router advertisement message 1010 ishalted.

At this time, as shown in FIG. 8 and FIG. 9A-FIG. 9D, not the homeaddress of router MR3 but home address MR2_HoA of router MR2 havingworked as the master router between mobile network 1 and home network 20is used as home address 603 of binding update message, and care ofaddress MR3_CoA is used as care of address 734 in binding update message700.

Router MR3 generates binding update message 700 including sequencenumber 621 which contains 1+the sequence number of sequence numberoption 1070, which sequence number has been notified by router MR2 withbinding message sequence number option 1070 of router advertisementmessage 1010. Router MR3 then transmits this binding update message 700to home agent HA6 (S1205), thereby registering its care of addressMR3_CoA as a primary care of address with home agent HA6 on home network20 of mobile network 1.

Home agent HA6 receives binding update message 700, then generatesbinding cache 1300 for associating home address MR2_HoA with care ofaddress MR3_CoA (S1206). This completes the preparation for forwardingor redirecting a packet to mobile network 1 after the movement of mobilenetwork 1 from home network 20 (S1207). FIG. 16 shows an instance ofbinding cache 1300 with which home address 1101, care of address 1302,lifetime 1103, flag 1104, sequence number 1105, and usage information1106 are associated with each other and registered.

Mobile router device MR2 has lost the connection to an external network,then halts the transmission of router advertisement message 1010 tomobile network 1, and router MR3 taking over the function of router MR2starts transmitting router advertisement message 1010 to the mobilenetwork. Thus after the lapse of valid lifetime 1040 included in thelast router advertisement message 1010 transmitted from router MR2, thedefault router of terminal device LFN5 is assigned to address MR3_In.

The packet transmitted by correspondent node device CN11 and addressedto terminal device LFN5 arrives at home gateway HGW7 based on the routeinformation in the Internet 8. Home gateway HGW7 forwards the packetaddressed to mobile network 1 to address MR2_HoA.

However, since home agent HA6 includes binding cache 1300 of MR2_HoA andcare of address MR3_CoA, home agent HA6 intercepts the packet, andencapsulates the packet addressed to terminal device LFN5, then forwardsto care of address MR3_CoA of mobile router device MR3. The packetencapsulated is delivered to mobile router MR3 via access router AR10,and decapsulated by MR3 before the packet is forwarded to terminaldevice LFN5.

On the other hand, terminal device LFN5 transmits a packet tocorrespondent node device CN11 this way: Terminal device LFN5 transmitsa packet addressed to correspondent node device CN11 to address MR3_Inof the default router, namely, mobile router device MR3. Router MR3receives the packet addressed to CN11, then encapsulates the packet andforwards the capsule to home agent HA6.

The packet encapsulated is delivered to home agent HA6 via access routerAR10, then decapsulated by home agent HA6. An examination of the packetaddress finds that the address does not belong to home network 20, sothat the packet is forwarded to correspondent node device CN11 via theInternet 8.

FIG. 4 shows a structure of mobile router devices MR2 and MR3. Each oneof those routers comprises the following elements:

-   -   physical interface to a backbone network 12;    -   L3 processing section 13;    -   physical interface to a mobile network 14;    -   Mobile IPv6 processing section 15; and    -   mobility management processing section 23.

Physical interface to a backbone network 12, carries out the followingprocesses: processes of the physical layer and the data link layer of apacket received from backbone network 8, process of transferring thepacket to L3 processing section 13, and process of providing the packet,received from L3 processing section and destined to backbone network 8,with data link process and physical layer process.

Physical interface to a mobile network 14, carries out the followingprocesses: physical layer process and data link layer process of apacket received from mobile network 1, process of transferring thepacket to L3 processing section 13, and process of providing the packet,received from L3 processing section and destined to mobile network 1,with data link process and physical layer process.

L3 processing section 13 carries out the following processes: providinga packet, transferred between physical interface to the backbone network12 or physical interface to the mobile network 14, with network layerprocess. On top of that, L3 processing section 13 generates routeradvertisement message 1010 and transmits/receives router advertisementmessage 1010, thereby monitoring the connection to the backbone networkand determining whether or not another mobile router device in themobile network works as a router for connecting the mobile network tothe backbone network. L3 processing section 13 also communicates withMobile IPv6 processing section 16 when Mobile IPv6 process is needed inthe packet.

Mobile IPv6 processing section 15 provides the packet received from L3processing section 13 with packet processing based on Mobile IPv6procedure, then transfers the packet to L3 processing section 13. MobileIPv6 processing section 15 receives a home address and a sequence numberfrom mobility management processing section 23, and generates a packetfor carrying out the mobility management of mobile network 1 based onthe home address, then transfers the packet to L3 processing section 13.

Mobility management processing section 23 receives the prefixinformation included in the router advertisement message from L3processing section 13, which information is received at the physicalinterface to the backbone network 12, and mobility management processingsection 23 records the prefix information in order to detect a movement.Mobility management processing section 23 also records the home addressto be used at physical interface to the backbone network 12, of a mobilerouter device in mobile network 1. Mobility management processingsection 23 further transfers the home address and the sequence number toMobile IPv6 processing section 15 because when a mobile router deviceconnects to an access network while moving, mobility managementprocessing section 23 manages the movement by using the home address.

A basic operation of mobile router device MR2 shown in FIG. 4 isdemonstrated hereinafter. Router MR2 forwards a packet in the followingmanner, and router MR3 has a similar structure and forwards a packet ina similar way to those of router MR2.

Mobile router device MR2 monitors the status of physical interface tothe backbone network 12. When router MR2 receives router advertisementmessage 1010 containing prefix information option 1030 and advertisementinterval option 1050, router MR2 determines that physical interface tothe backbone network 12 is connected to the backbone network. If routerMR2 does not receive the next router advertisement message 1010containing the same prefix 1043 even after the lapse of a predeterminedtime, router MR2 determines that physical interface to the backbonenetwork 12 lost the connection to the network.

At the same time, router MR2 determines a presence of a mobile routerdevice working as a mobile router connecting the mobile network to thebackbone network. To be more specific, if router advertisement message1010 from the mobile network is periodically transmitted by anotherrouter device, the mobile router device working as the mobile routerexists in the mobile network. If not, such a mobile router device doesnot exist.

Router MR2 works as a router device and transmits a packet betweenbackbone network 8 and mobile network 1 provided the following twoconditions are satisfied: physical interface to the backbone network 12,is connected to the backbone network; and there is only a mobile routerdevice that works as a mobile router which connects the mobile networkto the backbone network and no other such routers exist.

When mobile router device MR2 works as a router device, router MR2receives the packet received from backbone network 8, and the packetundergoes physical layer protocol process and data link protocol processin physical interface to backbone network 12. Then router MR2 forwardsthe packet to L3 processing section 13 where the packet undergoes IPprocess, while Mobile IPv6 processing section 15 carries out IP headerprocess, which is an additional part as Mobile IPv6 to IPv6, accordingto the Mobile IPv6 procedure. After the routing process in L3 processingsection 13, the packet is forwarded to one of physical interface to thebackbone network 12, or physical interface to the mobile network 14.

On the other hand, a packet received from mobile network 1 undergoes theprocess by physical interface to mobile network 14, and is forwarded toL3 processing section 13 where the packet undergoes IP protocol process,while Mobile IPv6 processing section 15 carries out IP header process,which is redundant to Mobile IPv6, according to the Mobile IPv6procedure. After the routing process in L3 processing section 13, thepacket is forwarded to one of physical interface to the backbone network12 or physical interface to the mobile network 14.

L3 processing section 13 generates router advertisement message 1010 inwhich prefix information option 1030 is stored in option field 1020, andforwards the message packet to physical interface to the mobile network14.

When router MR2 does not work per se as a router device, router MR 2disposes of a packet to be forwarded without any processes regarding thepacket. In this case router MR2 does not produce a router advertisementmessage. Further, physical interface to the mobile network 14, receivesa packet, which is then forwarded to L3 processing section 13, and thepacket is actually router advertisement message 1010 transmitted byanother mobile router device, and router advertisement message 1010contains binding message sequence number option 1070. In such a case,router MR2 notifies mobility management processing section 23 of thesequence number, and mobility management processing section 23 retainsthe sequence number.

FIG. 5-FIG. 7 describe how mobile router device MR2 updates the bindingwhen mobile network 1 leaves home network 20. FIG. 5 shows a flowchartillustrating the binding update procedure of mobile router device MR2.Mobility management processing section 23 examines prefix 1043 of prefixinformation option 1030 contained in router advertisement message 1010received L3 processing section 13 from physical interface to thebackbone interface 12. When this examination finds prefix 1043 differentfrom the prefix contained in the router advertisement message previouslyreceived, router MR2 detects that a connecting point to internet 8 ischanged, i.e. mobile network 1 moves (S51).

Detection of the movement prompts router MR2 to generate a care ofaddress using a virtual address and prefix information 1043 contained inrouter advertisement message 1010 (S52). After generation of the care ofaddress, router MR2 determines whether or not router MR2 per se works asa router device (S55). If router MR2 works as a router device, routerMR2 generates and transmits binding update message 600 shown in FIG. 6(S56).

Binding update message 600 comprises the following elements:

-   -   home address option 605 and mobility header 610 included in        extension header of IPv6 address option header;    -   binding update 620 included in a message data of the mobility        header; and    -   alternate care of address mobility option 630 included in a        mobility option of the binding update.        A number including 1+the sequence number retained by mobility        management processing section 23 is stored in sequence number        field 621 in binding update 620.

If router MR2 does not detect the movement of mobile network 1, routerMR2 determines whether or not L3 processing section 13 receives abinding acknowledgement message about the binding update messagetransmitted immediately before (S53). This determination is thenexamined whether or not the determination is carried out based on thelapse of the lifetime of the binding update message transmittedimmediately before (S54). In the case of router MR2 per se working as arouter device (S55), router MR2 generates and transmits binding updatemessage 600 when necessary (S56).

After the transmission of binding update message 600, mobilitymanagement processing section 23 updates its retaining sequence numberto the number stored in sequence number field 621 of binding updatemessage 600 transmitted.

In router MR2 working as a router device, when mobility managementprocessing section 23 determines that mobile network 1 moves, mobilitymanagement processing section 23 notifies L3 processing section 13 ofthe sequence number stored in sequence number 621 of binding updatemessage 600. L3 processing section 13 generates router advertisementmessage 1010 including prefix information option 1030 and bindingmessage sequence number option 1070 which stores the sequence numbernotified to binding message sequence number 1073. Router advertisementmessage 1010 is then forwarded to physical interface to mobile network14, then transmitted to mobile network 1 by physical interface to mobilenetwork 14.

Router MR2 can have such functions as generating and transmitting a datapacket by itself and receiving a data packet as a termination. In such acase, the structure can be what is shown in FIG. 10. This structure issimilar to what is shown in FIG. 4; however, it further includes upperlayer processing section 17 for carrying out upper layer processfollowing the protocol such as TCP or UDP, and application processingsection 18 for controlling an application.

A basic operation of mobile router device MR2 discussed above isdemonstrated hereinafter. Router MR 2 shown in FIG. 10 startstransmission this way: A transmission data generated by applicationprocessing section 18 for transmission to the Internet 8 is forwarded toL3 processing section 13, where an IP protocol process is carried out,via upper layer processing section 17 where process is carried outfollowing the protocol such as Sockets, TCP, or UDP. At the same time asthe IP process, Mobile IPv6 processing section 15, which carries out theprocess according to Mobile IPv6 procedure, carries out an IP headerprocess redundant to Mobile IPv6. The transmission data then undergoes adata link protocol process and a physical layer protocol process inphysical interface to the backbone network 12. The transmission data isfinally transmitted to backbone network 8.

Application processing section 18 of router MR2 generates thetransmission data for the transmission to mobile network 1, the data isforwarded to L3 processing section 13, via upper layer processingsection 17 where a process is carried out following the protocol such asSockets, TCP, or UDP. The transmission data then undergoes a data linkprotocol process and a physical layer protocol process in physicalinterface to the mobile network 14. The transmission data is finallytransmitted to mobile network 1.

Router MR2 receives data as a termination, and this reception operationis demonstrated hereinafter, namely, it is reverse to the transmissionoperation discussed above.

A packet received from backbone network 8 undergoes a physical layerprotocol process and a data link protocol process in physical interfaceto the backbone network 12, then undergoes the IP protocol process in L3processing section 13. During the IP protocol process, Mobile IPv6processing section 15 carries out a redundant IP header process at thesame time. Then the packet undergoes the process by upper layerprocessing section 17, and the packet is forwarded to applicationprocessing section 18.

After the packet received from mobile network 1 undergoes the physicallayer protocol process and the data link protocol process in physicalinterface to the mobile network 14, the packet undergoes the IP protocolprocess in L3 processing section 13. Then the packet undergoes theprocess by upper layer processing section 17, and the packet isforwarded to application processing section 18.

Meanwhile, this embodiment uses two mobile router devices and oneterminal device; however, not to mention, this embodiment can be appliedto the case where a greater number of devices are used.

As discussed above, in a mobile network to which plural mobile routerdevices attach, one of the addresses of the plural mobile router devicesis assigned as a common address to the mobile router devices' physicalinterface to the backbone network. A care of address corresponding tothis common address is used for binding update process, so that aterminal device in the mobile network having no Mobile IPv6 can carryout communications without increasing load to the mobile network whilethe terminal device moves among various access networks.

In this embodiment, the mobile router device working as a routernotifies another router device non-functional as a router of thesequence number used at the binding update. When the non-functionalrouter device starts working as a router, the sequence number notifiedis updated. A virtual address used by the former functional routerdevice is used for the binding update. In an environment where a mobilenetwork includes plural mobile router devices, and a mobile routerdevice is switched over to another one for connecting to the backbonenetwork, the foregoing mechanism allows the home agent to manage updatedmovement information about mobile network without paying attention to aswitch over of the mobile router device to another one. As a result,when a mobile network is provided with plural mobile router devices, thenetwork can move without incurring increment of load.

Exemplary Embodiment 2

FIG. 17 shows a structure of a mobile network in accordance with thesecond exemplary embodiment of the present invention. FIG. 17 shows anexample of mobile network 1 connected to home network 20. In thisexample, network 1 is connected to the Internet 8 (backbone network) viahome gateway 7. Mobile network 1 includes mobile router devices Mr2,MR3, and terminal device LFN5. Physical interfaces to the backbonenetwork of routers MR2 and MR3 can be the same ones or different ones.

The physical interface to backbone network 8 can adopt Ethernet method,IEEE802.11 (a, b, e, g, etc.) method, HIPERLAN method, IMT-2000 method,PDC method, GPRS method, or PHS method. Interfaces to the mobile networkcan adopt Ethernet method, Bluetooth method, Ultra Wide Band (UWB)method, or IEEE802.11 (a, b, e, g, etc.).

Routers MR2 and MR3 boot a virtual router redundancy protocol at theinterface to mobile network 1, to be more specific, they boot VRRP(virtual router redundancy protocol) for example.

In the example shown in FIG. 17, assume that the priority of determininga relation of master router vs. backup router in router MR2 is 100, thepriority of the same relation in mobile router device MR3 is 80. Therelation of master router vs. backup router on the physical interface tomobile network 1 is inherited to the physical interface to the backbonenetwork. The router working as a master router connects the backbonenetwork to the mobile network. In this embodiment, router MR2 works as amaster router, and router MR3 works as a backup router. They are shownwith solid lines and dotted lines respectively in FIG. 17.

The physical interface to mobile network 1 uses VRIP (MRi) as a virtualrouter address, and the physical interface to backbone network to homenetwork 20 uses VRIP (MRo) as a virtual router address. Both of themfollow IPv6 address format, e.g. the address of VRIP (MRi) is 3ffe:0501: : 5F00: 0202: 2cff: fe00: 000A, and the address of VRIP (MRo) is3ffe: 0501: : 0100: 0202: 2cff: fe00: 0001. Therefore, a default gatewayof terminal device LFN5 has an address of VRIP (MRi) and the next hop ofhome gateway HGW7 to mobile network 1 is VRIP (MRo).

When a packet is transmitted from correspondent node device CN11 toterminal device LFN5, the packet arrives at home gateway HGW7 based onroute information in the Internet 8. Home gateway HGW7 transmits apacket addressed to mobile network 1 to VRIP (MRo). Router MR2 workingas a master router forwards the packet addressed to terminal device LFN5to mobile network 1, so that the packet is delivered to terminal deviceLFN5.

On the other hand, terminal device LFN5 transmits a packet tocorrespondent node device CN11 this way: Terminal device LFN5 transmitsa packet addressed to correspondent node device CN11 to address VRIP(MRi) of the default router. Router MR2 working as the master routerreceives the packet addressed to CN11, then determines whether or notthe address of the packet belongs to home network 20. Sincecorrespondent node device CN11 does not attach to home network 20, thepacket is forwarded to the next hop, i.e. home gateway HGW7, which thenforwards the packet to the Internet 8 because the address of the packetdoes not belong to its home network 20. The packet is then delivered tocorrespondent node device CN11 via the Internet 8.

Backup router MR3 takes over the function of the master router andforwards the packet in the following cases: router MR2 becomes out oforder, router MR2 cannot receive router advertisement message 1010 froman access router connected to the backbone network, or router MR2 cannotfind an access link connecting to the backbone network and cannotforward the packet. In such a case, since the interface addresses stayunchanged as VRIP (MRo) and VRIP (MRi), terminal device LFN5 and homegateway HGW7 do not need any new process.

A connecting point to the Internet 8 is changed because of the movementof mobile network 1. A mobility management method in this case isdemonstrated with reference to FIG. 18 and FIG. 25. As shown in FIG. 18,mobile network 1 leaves home network 20 and attaches to access routerAR9 sharing the same physical link as the physical interface to backbonenetwork with mobile router device MR2 (S2101). At this time, router MR2receives a router advertisement message transmitted from access routerAR9 (S2102). Router MR2 generates care of address CoA_9(MR) to betemporarily used under router AR9 by using the prefix informationcontained in the router advertisement message (S2103). This care ofaddress can be produced, e.g. this way: the upper bits of the addressuse a prefix value obtained, and the lower bits use corresponding bitsof the virtual address.

FIG. 12 and FIG. 13A-FIG. 13D show a format of router advertisementmessage 1010. Router advertisement message 1010 includes prefixinformation option 1030 shown in FIG. 13B and advertisement intervaloption 1050 shown in FIG. 12 and FIG. 13C. In this second embodiment,router advertisement message 1010 needs not include binding messagesequence number option 1070 shown in FIG. 12 and FIG. 13D. Prefixinformation option 1030 stores prefix length 1033 and prefix information1043.

In the case of prefix length 1033 in prefix information option 1030being 64 bits, and prefix information 1043 being 3ffe: 0501: :1f00:3110: 5aff: fe00: 4326, care of address CoA_9(MR) generatedcorresponding to the VRIP (MRo) is 3ffe: 0501: : 1f00: 0202: 2cff: fe00:0001.

An instance of generating the care of address has been shown that thelower bits of the address to be generated use the same bits as thecorresponding bits of the virtual address; however, with respect to thislower bits, another generation method can be used, e.g. using randomnumbers.

Since router MR2 works as the master router, it generates binding updatemessage 1900 which stores home address VRIP (MRo) 1903, care of addressCoA_9(MR) 1934 as shown in FIG. 22 and FIGS. 23A-23D (S2104), thentransmits care of address CoA_9(MR) to home agent HA6 (S2105). As aresult, its care of address CoA_9(MR) is registered as a primary care ofaddress with home agent HA6 on home network 20.

Home agent HA6 receives binding update message 1900, then generatesbinding cache 2200 which associates home address VRIP(MRo) with care ofaddress CoA_9(MR) (S2106). This completes the preparation for forwardingor redirecting a packet to mobile network 1 after the movement of mobilenetwork 1 from home network 20 (S2107). FIG. 26 shows an instance ofbinding cache 2200 with which home address 2201, care of address 2202,lifetime 2203, flag 2204, sequence number 2205, and usage information2206 are associated with each other and registered.

The packet addressed to terminal device LFN5 and transmitted fromcorrespondent node device CN11 arrives at home gateway HGW7 based on theroute information in the Internet 8. Home gateway HGW7 transmits thepacket addressed to mobile network 1 to address VRIP(MRo). However,since home agent HA6 includes binding cache 2200 of VRIP(MRo) and careof address CoA_9(MR), home agent HA6 intercepts the packet, andencapsulates the packet addressed to terminal device LFN5, then forwardsto care of address CoA_9(MR) of mobile router device MR2. The packetencapsulated is delivered to mobile router MR2 via access router AR9,and decapsulated by router MR2 before the packet is forwarded toterminal device LFN5.

Next, when mobile router device MR2 cannot find a usable access link butmobile router device MR3 finds the usable access link, what kind ofmobility management method is taken is demonstrated hereinafter withreference to FIG. 19 and FIG. 27.

Mobile router devices MR2 and MR3 change their priorities in response totheir connection status to backbone network 8. When they can beconnected to backbone network 8, a regular priority is used; however asthe connection becomes degraded due to, e.g. receiving signal strengthbecomes weaker, or unable to receive a periodical router advertisementmessage, the priority is lowered in response to the bandwidth of thenetwork. If no connection is obtained at all, the priority is lowered tozero (0). At this time, if router MR3 can obtain a connection, routerMR3 gets a higher priority, and the master router is switched fromrouter MR2 to router MR3.

As shown in FIG. 19, assume that mobile network 1 leaves access network21 and moves under access router AR10 having the physical link as sameas the MR3's physical interface to the backbone network (S2301). At thistime, the connection between router MR2 and backbone network 8 degrades,and router MR2 cannot receive router advertisement message 1010 fromaccess router AR9 (S2310); however, router MR3 receives routeradvertisement message 1010 from access router AR10 (S2302).

Router MR3 obtains prefix information 1043 from router advertisementmessage 1010, and generates care of address CoA_10(MR) to be temporarilyused under access router AR10 (S2303). For instance, in the case ofprefix length 1033 in prefix information option 1030 contained in routeradvertisement message 1010 being 64 bits, and prefix information 1043being 3ffe: 0501: :2f00: 3110: 5aff: fe00: 4326, care of addressCoA_10(MR) generated corresponding to the VRIP (MRo) is 3ffe: 0501: :2f00: 0202: 2cff: fe00: 0001. As discussed previously, routers MR2 andMR3 change their priorities in response to the connection status to thebackbone network. When the priority of router MR3 becomes higher thanthat of router MR2, the function of the master router is taken over byrouter MR3 (S2304).

Since router MR3 works as the master router, it generates binding updatemessage 1900 which stores home address VRIP (MRo) 1903, care of addressCoA_10(MR) 1934 as shown in FIG. 22 and FIG. 23A (S2305), then transmitsit to home agent HA6 (S2306). As a result, its care of addressCoA_10(MR) is registered as a primary care of address with home agentHA6 on the home link of router MR3.

Home agent HA6 receives binding update message 1900 from mobile routerdevice MR3, then updates the binding cache entry of home address VRIP(MRo) to binding cache 2400 that associates home address VRIP (MRo) withcare of address CoA_10(MR) (S2307), thereby completing a forwardingpreparation for the case where the mobile router device, which isexpected to connect mobile network 1 to backbone network 8, is switchedto another one (S2308).

In the case of transmitting a packet from correspondent node device CN11to terminal device LFN5, the wording of the description about the casewhere mobile network 1 is governed by access router AR9 is replaced withthe wording of the case where mobile network 1 is governed by accessrouter 10. To be more specific, care of address CoA_9(MR) is replacedwith CoA_10(MR), so that the subject case can be appropriatelydescribed. Thus the detailed description thereof is omitted here.

FIG. 20 shows a structure of mobile router devices MR2 and MR3. Each oneof the mobile router devices comprises the following elements:

-   -   physical interface to the backbone network 12;    -   L3 processing section 13;    -   physical interface to a mobile network 14;    -   mobile Ipv6 processing section 15;    -   virtual router processing section 16; and    -   mobile management processing section 23.    -   Physical interface to a backbone network 12 carries out the        following processes: processes of the physical layer and the        data link layer of a packet received from backbone network 8,        process of transferring the packet to L3 processing section 13,        and process of providing the packet, received from L3 processing        section and destined to backbone network 8, with data link        process and physical layer process. On top of those processes,        interface 12 further monitors link quality indicating connection        status to backbone network 8, and transfers the connection        status information to virtual router processing section 16.

Physical interface to a mobile network 14 carries out the followingprocesses: physical layer process and data link layer process of apacket received from mobile network 1, process of transferring thepacket to L3 processing section 13, and process of providing the packet,received from L3 processing section and destined to mobile network 1,with data link process and physical layer process.

L3 processing section 13 carries out the following processes: providinga packet, transferred via physical interface to the backbone network 12or physical interface to the mobile network 14, with network layerprocess. L3 processing section 13 transfers the packet to Mobile IPv6processing section 15 if the packet needs Mobile IPv6 process, andtransfers the packet to virtual router processing section 16 if thepacket needs a virtual router redundancy protocol process. Further, L3processing section 13 receives the information about whether or not themobile router device works as the master router from virtual routerprocessing section 16, and when the device works as the master router,it takes a necessary procedure.

Mobile IPv6 processing section 15 provides the packet received from L3processing section 13 with a packet process based on Mobile IPv6procedure, then transfers the packet to L3 processing section 13. MobileIPv6 processing section 15 receives a virtual address and a sequencenumber from mobility management processing section 23, and generates apacket for carrying out the mobility management of mobile network 1based on the virtual address, then transfers the packet to L3 processingsection 13.

Virtual router processing section 16 carries out the process, based on avirtual router redundancy protocol, for both of the mobile routerdevices MR2 and MR3 working virtually as a single router in mobilenetwork 1. The process includes the following processes: changing apriority based on the connection status information obtained fromphysical interface to the backbone network 12; generating a virtualrouter advertisement packet and transmitting to L3 processing section13; receiving a virtual router advertisement packet from L3 processingsection 13; and recording the information about whether or not therouter device works as the master router into mobility managementprocessing section 23. Besides those processes, virtual routerprocessing section 16 transfers a sequence number contained in thevirtual router advertisement packet to mobility management processingsection 23.

Mobility management processing section 23 records an address to bevirtually used at physical interface to the backbone network 12 of amobile router device in mobile network 1, and retains the sequencenumber received from virtual router processing section 16. When themobile router device receives the information about whether or not therouter per se works as the master router and determines the router perse is the master router, mobility management processing section 23further transfers the virtual address and the sequence number to MobileIPv6 processing section 15 in order to manage the movement by using thevirtual address.

A basic operation of mobile router device MR2 shown in FIG. 20 isdemonstrated hereinafter. Router MR2 forwards a packet in the followingmanner, and router MR3 has a similar structure and forwards a packet ina similar way to those of router MR2.

Mobile router device MR2 monitors its own status managed by virtualrouter processing section 16, and recognizes whether or not router MR2per se works as the master router. In the case of router MR2 working asthe master router, router MR2 receives the packet received from backbonenetwork 8, and the packet undergoes physical layer protocol process anddata link protocol process in physical interface to backbone network 12.Then router MR2 forwards the packet to L3 processing section 13 wherethe packet undergoes IP process, while Mobile IPv6 processing section 15carries out IP header process, which is redundant to Mobile IPv6,according to the Mobile IPv6 procedure. After the routing process in L3processing section 13, the packet is forwarded to one of physicalinterface to the backbone network 12 or physical interface to the mobilenetwork 14.

On the other hand, a packet received from mobile network 1 undergoes theprocess by physical interface to mobile network 14, and is forwarded toL3 processing section 13 where the packet undergoes IP protocol process,while Mobile IPv6 processing section 15 carries out IP header process,which is redundant to Mobile IPv6, according to the Mobile IPv6procedure. After the routing process in L3 processing section 13, thepacket is forwarded to one of physical interface to the backbone network12 or physical interface to the mobile network 14.

When router MR2 works per se as a backup router, router MR 2 disposes ofa packet to be forwarded without any processes regarding the packet.

FIG. 21-FIG. 23 describe how mobile router device MR2 updates thebinding when mobile network 1 leaves home network 20. FIG. 21 shows aflowchart illustrating the update procedure of mobile router device MR2.When router MR2 detects the movement of mobile network 1 (S51), routerMR2 generates a care of address by using prefix information 1043contained in router advertisement message 1010 and the virtual address(S52). After the generation of the care of address, router MR2determines whether or not it works as the master router (S181). In thecase of router MR2 working as the master router, router MR2 generatesand transmits binding update message 1900 shown in FIG. 22 (S182).

Binding update message 1900 comprises the following elements:

-   -   home address option 1905 and mobility header 1910 included in        extension header of IPv6 address option header;    -   binding update 1920 included in a message data of the mobility        header; and    -   alternate care of address option 1930 included in a mobility        option of the binding update.        Home address option 1905 stores the virtual address instead of        the home address of the router per se in home address field        1903. V-flag 1922 indicating the transportation of the virtual        address is newly prepared in binding update 1920.

If router MR2 does not detect the movement of mobile network 1, routerMR2 determines whether or not L3 processing section 13 receives abinding acknowledgement message about the binding update messagetransmitted immediately before (S53). This determination is thenexamined whether or not the determination is carried out based on thelapse of the lifetime of the binding update message transmittedimmediately before (S54). In the case of router MR2 per se working as amaster router (S181), router MR2 generates and transmits binding updatemessage 600 when necessary (S182).

After the transmission of binding update message 600, mobilitymanagement processing section 23 updates its retaining sequence numberto the number stored in sequence number field 621 of binding updatemessage 600 transmitted.

Meanwhile, the detection of movement in S51 is applicable not only tothe case where the node to the Internet 8 is changed due to the movementof mobile network 1, but also to another case where the operation ofrouter MR2 is physically changed from a backup router to a master routerdue to the virtual router redundancy protocol booted on the side ofmobile network 20.

The function of a master router is transferred from router MR2 to routerMR3 due to degradation of the link environment. The procedure of such acase is described hereinafter with reference to FIG. 29 illustrating asequence in accordance with the virtual router redundancy protocol. Inthe first place, router MR2 works as a master router, and router MR3works as a backup router.

Mobile router device MR2 working as the master router periodicallytransmits a virtual router advertisement packet including VRRP field2600 shown in FIG. 30 from physical interface to the mobile network 14(S2501). This packet includes priority information of mobile routerdevices and an advertisement interval. If the priority information inthe packet is lower than the priority of the backup router or the backuprouter does not receive the virtual router advertisement packet within agiven time predetermined in response to the advertisement interval, amobile router device working as a backup router determines that thepresent master router is not fit for the function, so that it takes overthe master router by itself.

If the movement of mobile network 1 causes degradation of the quality ofthe communication link between router MR2 and access router AR9, thepriority is lowered by virtual router processing section 16 in routerMR2 (S2502). Router MR2 stores the priority lowered due to thedegradation of the link quality, and still transmits periodically thevirtual advertisement packet (S2503).

When receiving the virtual advertisement packet, router MR3 refers tothe priority information in the virtual router advertisement packet, andverifies whether or not the priority is lower than that of itself. Ifthe priority of itself is higher than that stored in the packet, routerMR3 takes over the function of the master router (S2504).

Mobile router device MR3 taking over the function of the master routertransmits periodically the virtual router advertisement packet, whichcontains its own priority, from physical interface to the mobile network14 (S2505).

When router MR2 receives the virtual router advertisement packet whichcontains the priority higher than its own priority (S2505), router MR2becomes a backup router (S2506), and stops transmitting the virtualadvertisement packet as well as processing as the master router.

The VRRP field of the virtual router advertisement packet in accordancewith this second exemplary embodiment has M-flag 2605 shown in FIG. 30,which M-flag a conventional VRRP field does not have. When this bit isset, a virtual redundant router works in the mobile router device, andthis work indicates that VRRP field 2600 contains sequence number field2613. A value stored in sequence number field 1921 at binding updatemessage 1900 produced immediately before is stored in sequence numberfield 2613. In the case of a switchover of the master router, the valueof sequence number field 2613 is added by 1 (one), then put into bindingupdate message 1900.

Router MR2 can have a function of generating and transmitting a datapacket by itself as well as a function of receiving a data packet as atermination. FIG. 24 shows a structure in such a case. This structure isbasically similar to what is shown in FIG. 20; however, this structurefurther includes upper layer processing section 17, which carries outthe process of upper layers such as TCP and UDP, and applicationprocessing section 18.

A basic operation of foregoing mobile router MR2 is demonstratedhereinafter: Router MR2 shown in FIG. 24 starts transmitting in thefollowing manner: Transmission data generated by application processingsection 18 for transmission to the Internet 8 is forwarded to L3processing section 13, where IP protocol process is carried out, viaupper layer processing section 17 where process is carried out followingthe protocol such as Sockets, TCP, or UDP. At the same time as the IPprocess, Mobile IPv6 processing section 15, which carries out theprocess according to Mobile IPv6 procedure, carries out IP headerprocess redundant to Mobile IPv6. The transmission data then undergoesdata link protocol process and physical layer protocol process inphysical interface to the backbone network 12. The transmission data isfinally transmitted to backbone network 8.

At this time, the source address uses the care of address correspondingto the original home address or the original home address per se forcarrying out a communication, so that the binding update process for thecare of address is processed by a regular Mobile IPv6 process regardlessof a master or a backup specified by the virtual router redundancyprotocol.

Application processing section 18 of router MR2 generates thetransmission data for the transmission to mobile network 1, the data isforwarded to L3 processing section 13, via upper layer processingsection 17 where process is carried out following the protocol such asSockets, TCP, or UDP. The transmission data then undergoes a data linkprotocol process and a physical layer protocol process in physicalinterface to the mobile network 14. The transmission data is finallytransmitted to mobile network 1.

Router MR2 receives data as a termination, and this reception operationis demonstrated hereinafter, namely, it is reverse to the transmissionoperation discussed above.

A packet received from backbone network 8 undergoes a physical layerprotocol process and a data link protocol process in physical interfaceto the backbone network 12, then undergoes an IP protocol process in L3processing section 13. During the IP protocol process, Mobile IPv6processing section 15 carries out a redundant IP header process at thesame time. Then the packet undergoes the process by upper layerprocessing section 17, and the packet is forwarded to applicationprocessing section 18.

After the packet received from mobile network 1 undergoes the physicallayer protocol process and the data link protocol process in physicalinterface to the mobile network 14, the packet undergoes the IP protocolprocess in L3 processing section 13. Then the packet undergoes theprocess by upper layer processing section 17, and the packet isforwarded to application processing section 18.

Meanwhile, this embodiment uses two mobile router devices and oneterminal device; however, not to mention, this embodiment can be appliedto the case where a greater number of devices are used.

As discussed above, in a mobile network to which plural mobile routerdevices attach, a virtual address is used to the mobile router devices'physical interface to the backbone network. A virtual router redundancyprotocol is booted at the physical interface to a mobile network. Thevirtual address of the physical interface to the backbone network andthe care of address corresponding to this virtual address are used forbinding update process, so that a terminal device in the mobile networkhaving no Mobile IPv6 can carry out communications without increasingload to the mobile network while the terminal device moves among variousaccess networks.

INDUSTRIAL APPLICABILITY

In the case of providing plural mobile router devices which are capableof connecting the mobile network to an access network, the presentinvention achieves to switch a mobile router device to another onewithout increasing load to the network. The present invention isapplicable to a mobile network system that moves among different accessnetworks in a backbone network considered as a whole to be one network.

LIST OF REFERENCE MARKS IN DRAWINGS

-   1 mobile network-   2, 3 mobile router device-   5 terminal device-   6 home agent-   7 home gateway-   8 the Internet-   9, 10 access router-   11 correspondent node device-   12 physical interface to backbone network-   13 L3 processing section-   14 physical interface to mobile network-   15 Mobile IPv6 processing section-   16 virtual router processing section-   17 upper layer processing section-   18 application processing section-   20 home network-   21, 22 access network-   23 mobility management processing section

1. A mobile router device, to which at least one terminal deviceattaches, connects a backbone network to a mobile network moving withinthe backbone network, the mobile router device comprising: a means fordetermining whether or not the mobile router device works as a masterrouter that can connect the mobile network to the backbone network; ameans for recording a virtual address common to respective mobile routerdevices attaching to the mobile network, and producing a care of addresswith respect to the virtual address and usable by the mobile routerdevice per se at a location to which the router device moves; and ameans for generating and transmitting a binding update message whichmakes the virtual address corresponding to the care of address when themobile router device works as the master router.
 2. The mobile routerdevice of claim 1, wherein the virtual address is used as a real addressassigned to any one of the respective mobile router devices attaching tothe mobile network.
 3. The mobile router device of claim 1 furthercomprising: a means for monitoring quality of a link connected to thebackbone network; a means for changing a priority which determines themaster router and a backup router in response to the quality of thelink; and a means for determining whether or not the mobile routerdevice per se works as the master router in response to the priority. 4.The mobile router device of claim 1 further comprising a means forstoring a sequence number of the binding update message into a masterrouter advertisement packet and for transmitting the packet when themobile router device works as the master router.
 5. The mobile routerdevice of claim 4, wherein the master router advertisement packet uses avirtual router advertisement in accordance with a virtual routerredundancy protocol.
 6. The mobile router device of claim 4, wherein themaster router advertisement packet uses IPv6 router advertisementmessage.
 7. The mobile router device of claim 1 further comprising: ameans for receiving a master router advertisement packet which istransmitted by another mobile router device and notifies the mobilerouter device of the another mobile router device working as the masterrouter; and a means for recording a sequence number of the bindingupdate message contained in the master router advertisement packetreceived in order to use the sequence number for a case when the mobilerouter device per se becomes the master router, when the mobile routerdevice works as a backup router.
 8. The mobile router device of claim 7,wherein the master router advertisement packet uses a virtual routeradvertisement in accordance with a virtual router redundancy protocol.9. The mobile router device of claim 7, wherein the master routeradvertisement packet uses IPv6 router advertisement message.
 10. Amobile network system comprising: a plurality of the mobile routerdevices as defined in claim 1; at least one terminal device attaching tothe mobile router devices; and a home agent device for managingmovements of the mobile router devices.
 11. The mobile network system ofclaim 10, wherein at least one of the mobile router devices has aphysical interface to a backbone network, a type of which interface is adifferent from those of other mobile router devices.
 12. The mobilenetwork system of claim 10, wherein each one of the mobile routerdevices uses a virtual address common to the others at a side to abackbone network and implements a virtual router redundancy protocol ata side to a mobile network, wherein when one of the mobile routerdevices works as a master router, the master router uses the commonvirtual address for communication.
 13. The mobile network system ofclaim 12, wherein one of the mobile router device working as the masterrouter uses the common virtual address and a care of address generatedcorresponding to the common virtual address for transmitting a bindingupdate message to be used for a mobility management to the home agentdevice.
 14. A mobility management method of a mobile router deviceattaching to a mobile network system, which system comprising: at leastone terminal device; a mobile network including a plurality of mobilerouter devices, to which the terminal device attaches, for coupling themobile network to a backbone network; and a home agent device forassociating a home address with a care of address and managing both ofthe addresses, wherein when the mobile network is connected to a homenetwork and when one of the mobile router devices working as a masterrouter is to still work as the master router after a movement, themanagement method associates a care of address corresponding to avirtual address generated after the movement with the virtual addressand registers the care of address with the home agent device, or whenone of the mobile router devices working as a backup router is to becomethe master router after the movement, the managing method associates thecare of address corresponding to the virtual address generated after themovement with the virtual address and registers the care of address withthe home agent device.
 15. The mobility management method as defined inclaim 14, wherein the virtual address is any one of physical addressesto be used in physical interfaces, to the backbone network, when eachone of the mobile router devices attaching to the mobile network isconnected to the home network.
 16. The mobility management method asdefined in claim 14, wherein the method puts the virtual address and asequence number of a binding update message to be transmitted to thehome agent device into a master router advertisement packet to betransmitted to the mobile network for notifying the home agent device ofthe mobile router device being to work as the master router.
 17. Themobility management method as defined in claim 16, wherein the masterrouter advertisement packet is a virtual router advertisement packet tobe used by a virtual router redundancy protocol implemented in themobile router device at a side to the mobile network.
 18. The mobilitymanagement method as defined in claim 16, wherein the master routeradvertisement packet includes IPv6 router advertisement message to betransmitted from the mobile router device working as the master routerto a side of the mobile network of the mobile router device.